I suggest you look into WMI (Windows Management Instrumentation). You can get some info plus a free tool to explore WMI from this site. Here is a direct link to the download. More info is available here.

ReverendJim, that tool looks nice, I'll have to check that out myself.

Another suggestion, is you could always look on how others do it. There is CUPID as well as Open Hardware Monitor. They both offer the source code or a dev code that you can look at (note that CUPID, my Nortan loves to flag the dev code, so I'd watch that one)